Fundamentals of Radio Wave Propagation.pptx

Discusses the fundamental characteristics of waves

1. Radio wave propagation Optical Characteristics Propagation through space Common propagation problems Cervantes, Mary joy Neverio , Fulgencio Estallo , Michael BSECE-2C

2. Radio waves Act very much as light waves do Can be reflected, refracted, diffracted, and focused by other objects

3. Optical characteristics Reflection Note: The angle of reflection is equal to the angle of incidence The angle of incidence is the angle between the incoming line of the wave and a perpendicular line to the reflecting surface The angle of reflection is the angle between the reflected wave and the perpendicular line

4. Optical characteristics Refraction Index of Refraction (n) Is the bending of a wave due to the physical makeup of the medium through which the wave passes The ratio of the speed of radiation (as light) in one medium (as air, glass, or a vacuum) to that in another medium Snell’s Law n 1 sin θ 1 = n 2 sin θ 2 w here n 1 = index of refraction of initial medium θ 1 = angle of incidence n 2 = index of refraction of initial medium θ 2 = angle of refraction

5. Optical characteristics Diffraction Is the spreading out of waves through an aperture or around objects Explained by what is known as Huygen’s Principle which is based on the assumption that all electromagnetic waves, light as well as radio waves, radiate as spherical wave fronts from a source Diffraction causes waves to bend around obstacles

6. Propagation through space Three basic paths that a radio signal can take Ground Wave Ground wave radiation from an antenna It follows the curvature of the earth and can, therefore, travel at distances beyond the horizon Strongest at the low- and medium-frequency ranges The conductivity of the earth determines how well ground waves are propagated The better the conductivity, the less the attenuation and the greater the distance the waves can travel

7. Propagation through space Three basic paths that a radio signal can take Sky Wave Sky wave propagation Are radiated by the antenna into the upper atmosphere where they are bent back to earth This bending of the signal is caused by refraction in a region known as the ionosphere T he different levels of ionization causes the radio waves to be gradually bent The direction of bending depends on the angle at which the radio wave enters the ionosphere, as determined by Snell’s Law

8. Propagation through space Three basic paths that a radio signal can take Space Wave Line-of-sight communication Travels in a straight line directly from the transmitting antenna to the receiving antenna Are not refracted, nor do they follow the curvature of the earth The formula for computing the distance between a transmitting antenna and the horizon is This is called the radio horizon. w here h t = height of transmitting antenna, ft d = distance from transmitter to horizon

9. Common propagation problems Fading Multipath Is the variation in signal amplitude at the receiver caused by the characteristics of the signal path and changes in it Causes the receives signal to vary in amplitude, typically making it smaller Caused by four factors: variation in distance changes in the environmental characteristics presence of multiple signal paths relative motion between the transmitter and the receiver Occurs when a transmitted signal takes multiple paths to the receiver because of reflections